Fluorescent lamps are widely used in a variety of locations, such as schools and office buildings. Although conventional fluorescent lamps have certain advantages, they also pose certain disadvantages, including disposal problems due to the presence of toxic materials within the tube. LED-based lamps, or LED tubes, which can be used as one-for-one replacements for fluorescent tube lamps, have emerged in recent years. Such LED-based replacement lamps typically include an elongate housing, with LEDs mounted on a circuit board inside the housing. An endcap is arranged at each longitudinal end of the housing for connecting the LED circuit board to the luminaire.
It has been observed that, after the use over a certain time period (e.g. a few months), a problem of overheating can occur in some of these LED lamps. Such overheating sometimes causes the LED lamp to melt, or even results in fire and burn hazards.
The inventors have identified that arcing is a cause of this problem. Arcing, or arc discharge, is an electrical breakdown of a gas that produces an ongoing electrical discharge. This occurs when two or more conductors in a circuit are not properly contacted. When there is a small gap between these conductors, the voltage across them could break down the gas resistance and create a current—as a small scale lightning. This current is typically high enough to increase the temperature of the components of the LED lamp, e.g. the circuit board of LEDs. This increase of temperature entails the risk of the melting of the LED lamp and the risk of fire and burn hazards.
Arcing is not assumed to occur in those lamps most LED lamps are carefully designed to avoid the presence of any small gap between conductors. According to the design of these lamps, all conductors are expected to be properly in contact with each other. Nevertheless, arcing still occurs after a certain time of use.
As recognized by the inventors, this unexpected behavior lies in an unexpected interaction between some safety mechanism in modern LED tubes and the fixture of the luminaire.
User safety is an important aspect when designing LED tubes. If the lamp fixture is energized when the LED tube is not yet completely installed into the fixture, and the user happens to grab the LED tube in a wrong position, electrical current can flow through the user's body and hurts the user. To avoid this risk, there are usually safety mechanisms in LED lamps which allow the connector pins and the circuit board of LEDs temporarily disconnected. Such mechanisms are typically designed in accordance with the standard size of the lamp fixture. However, a side-effect has been observed by the inventors that the safety mechanism can increase the pressure applied on the fixture of the luminaire. Due to this increased pressure, the distance between two ends of the fixture can increase over time. When the distance reaches a certain point, a gap can be created between the connector pins of the endcap and the LED circuit board, or between the connector pins and the connectors in the fixture. From there, arcing can occur.